The present invention pertains to a space conditioning system for controlling the humidity of air in an enclosed space using reheat of recirculated air and introducing ambient outdoor air if the enthalpy of the outdoor air is suitable for meeting the dehumidification demand of the system.
Space conditioning systems, including air systems which utilize vapor compression cooling of recirculated air, often require relatively accurate control of the humidity in the air in the conditioned space. Air conditioning systems are known of the type which use a vapor compression refrigeration circuit to cool and dehumidify the air entering the enclosed air conditioned space and which also utilize a heat exchanger in the air flowpath to reheat the air after the air has been cooled and dehumidified by the refrigeration circuit.
In one such system, as described in U.S. Pat. No. 5,622,057, a heat exchanger is positioned downstream of the evaporator to subcool the refrigerant before it enters the evaporator to enhance dehumidification of the air passing through the evaporator and to reheat the air after it passes through the evaporator. A major disadvantage of this type of system is that dehumidification of the air supplied to an indoor space occurs only when there is a cooling demand.
Another disadvantage of prior art air conditioning systems using vapor compression is that more energy input is required to provide the required cooling, dehumidification and reheat of the circulated air because the air must be cooled below the temperature required to meet the cooling demand in order to dehumidify the air and then reheated to a desired temperature.
The present invention provides a system and method for providing cooled and dehumidified air to an enclosed space which overcomes certain deficiencies of known systems.
The present invention provides an improved space conditioning system for cooling and dehumidifying air in an enclosed space.
In accordance with one important aspect of the invention, a space conditioning system is provided which utilizes refrigerant cooling and reheat of recirculated air or alternatively utilizes ambient outdoor air to control the humidity of the air in an enclosed space serviced by the system. In particular, the system preferably includes a vapor compression refrigeration unit wherein humidity control is provided by cooling, dehumidifying and then reheating recirculated air and wherein the reheating step is accomplished by passing the treated air through a reheating coil comprising part of the condenser circuit of the vapor compression refrigeration unit.
In accordance with another aspect of the invention a space conditioning system is provided wherein ambient outdoor air may be selectively controlled for introduction into the air being circulated to the enclosed space to control humidity in the space if the ambient outdoor air enthalpy is within a range which will provide the required dehumidification. In this regard, an enthalpy sensor is operable to sense the total enthalpy of the ambient outdoor air and a signal from the enthalpy sensor is used by a programmable controller to determine whether or not to use outdoor air for dehumidification or to use the vapor compression refrigeration unit to cool, dehumidify and reheat air being circulated to the enclosed space to control the relative humidity thereof. Dehumidification is accomplished even in the absence of a demand for space cooling.
The present invention further provides a space conditioning system which includes a control circuit wherein priority is given to meeting the cooling or heating demand of the system regardless of the humidity requirements. Under circumstances of responding to a temperature setpoint sensor (thermostat) the system will shut off flow of heated refrigerant gas to a reheat heat exchanger or coil in order to meet the air cooling requirements for the air being circulated through the enclosed space.
Still further, the invention provides a system which utilizes either relatively dry outdoor air or mechanical refrigeration to dehumidify a conditioned space when there is a demand for reducing the humidity in the enclosed space. The system includes a controller which chooses the dehumidification method, either reheat of cooled and dehumidified air or introducing ambient outdoor air into the airflow circuit. The system may comprise an otherwise substantially conventional air conditioning system which is modified to provide controls for introduction of outdoor air into the recirculated or return air circuit and also a circulated air reheat heat exchanger and control valve for controlling the flow of compressed refrigerant fluid.
In accordance with yet another aspect of the invention, a supply air sensor (which may be a temperature sensor or an enthalpy sensor) is used to control the relative proportions of return air from the space and outdoor ambient air by measuring a characteristic (temperature or enthalpy) of the air supplied to the space when dehumidification is being accomplished using ambient outdoor air instead of the reheat method using the vapor compression unit.
Those skilled in the art will further appreciate the above-mentioned features and advantages of the invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings.